I have a player whose character has a large family. They are wanting to play one of the same character's children for another line they would like to bring in. They have said that they will not play 'with themselves' as in one on one scenes with those characters for AC, that all - or at least most - interaction with the characters will be in group scenes. I can't see a reason to say no to the request, but I just wanted to get some perspective. I will add there are two other family members in game, as well as the line they are planning with a different character which is why they want to bring the new character in, so I don't have any worries that they will end up using this situation to fudge on AC.